The invention relates to novel monoazo dyes and their salts, a method of their preparation and their use in dying and printing operations. It relates also to liquid dye preparations containing these dyes, particularly to aqueous inks for ink jet printing.
Ink jet printing processes are essentially of two types:
In continuous stream ink jet printing systems, ink is emitted in a continuous stream under pressure through a nozzle. The stream breaks up into droplets at a certain distance from the nozzle. If a specific location on the recording sheet has to be printed the individual droplets are directed to the recording sheet, otherwise they are directed to a gutter. This is done for example by charging unnecessary droplets in accordance with digital data signals and passing them through an electrostatic field which adjusts the trajectory of these droplets in order to direct them to the gutter. The inverse procedure may also be used wherein uncharged droplets are directed to the gutter.
In the non-continuous process, or the so-called xe2x80x9cdrop-on-demandxe2x80x9d systems, droplets are generated in accordance with digital data signals only if a specific location on the recording sheet has to be printed.
The speed of ink jet printers of the newest generation is, for economic reasons, ever increasing. Digital images, captured with digital cameras or generated by scanning of silver halide camera films, may be printed with these modern printers with a quality level that make them nearly indistinguishable from classical copies on silver halide materials. Images produced in this way need to have an excellent storage stability even under adverse conditions. This can only be achieved by using a finely tuned system of inks (respectively the dyes contained therein) together with a suitable recording sheet.
Recording sheets particularly suitable for these printers and photo realistic recordings need to absorb the inks very rapidly. The recording sheets comprise organic polymers and/or microporous inorganic oxides. Up to now the produced images do not have all the properties required. Particularly the diffusion fastness of images printed onto such recording sheets under conditions of high temperature and humidity is unsatisfactory. Images printed onto such recording sheets, using inks containing dyes that are state of the art, lose their sharpness under the influence of heat and humidity or show uncontrollable density changes or color shifts. Therefore, there is a need for dyes with excellent diffusion fastness in order to increase the diffusion fastness of images printed onto these recording sheets under conditions of high humidity and heat.
Although quite a number of different dyes have already been proposed as dyes for ink jet printing, none meets all the necessary requirements.
The magenta dye of formula (I) (Example No. 2) is described in U.S. Pat. No. 5,542,970. 
The magenta dye of formula (II) (Example No. 1) is described in U.S. Pat. No. 5,254,160. 
The magenta dye of formula (III) (Example No. 1) is described in patent application JP 03-203,970. 
All these dyes, representing the state of the art, do not satisfy all the required demands if they are used in the formulation of inks for ink jet printing that should provide brilliant images or colorings with excellent color rendition (extended gamut) on any type of recording sheet as plain or coated paper, coated or uncoated, opaque or transparent synthetic materials, because these dyes diffuse under conditions of high temperature and humidity and the sharpness of the images is deteriorated.
Dyes used for such recording liquids need to have a good solubility in the essentially aqueous ink liquid, they have to penetrate into the recording sheet and should not show dye aggregation on the surface of the recording sheet (xe2x80x9cbronzingxe2x80x9d). They need to provide printed images having high optical density, good water fastness, good light stability and good storage stability even under adverse conditions. They need to be stable in the ink even when the recording liquid is stored for a long time under adverse conditions.
Various types of compositions have been proposed as inks for ink jet printing. Typical inks comprise one or more dyes or pigments, water, organic cosolvents and other additives.
The inks have to meet the following criteria:
(1) The ink gives images of excellent quality on any type of recording sheet.
(2) The ink gives printed images exhibiting good water fastness.
(3) The ink gives printed images exhibiting good light stability.
(4) The ink gives printed images exhibiting excellent smudge behavior.
(5) The ink gives printed images exhibiting excellent storage stability under conditions of high temperature and humidity.
(6) The ink does not clog jetting nozzles of the ink jet printers even when these are kept uncapped while recording is suspended for long periods.
(7) The ink may be stored for long periods of time without deterioration of its quality.
(8) The values of the physical properties of the inks, such as viscosity, conductivity and surface tension are all within defined ranges well suited for the intended use.
(9) The ink has to be non-toxic, not flammable and safe.
Accordingly, an object of the invention is to provide novel monoazo dyes with a red or magenta hue and showing, at the same time, excellent light stability, water fastness, diffusion fastness and high solubility. They provide images or colorings showing good overall properties, in particular in the ink jet printing process, where they provide images with maximum color rendition, and where the sharpness of the images does not or only slightly deteriorate during long periods of storage under conditions of high temperature and humidity.
Another object of the invention is the provision of liquid dye preparations, especially of recording liquids for ink jet printing, showing a spectrally unchanged hue on any type of recording sheet as plain or coated paper, coated or uncoated, opaque or transparent synthetic materials.
A further object of the present invention is the provision of inks satisfying all the requirements mentioned above.
In the present invention, these purposes, as well as others which will be apparent, are achieved generally by providing novel monoazo dyes of general formulas (IV) and (V) detailed below.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description of the invention when considered with reference to the drawings, as follows: